Patent GB-1454503-A (GB)
Title: Asbestos reinforced plastics materials
IPC: D02G3/20
Filed: 1972-12-29
Abstract: 1454503 Laminates TBA INDUSTRIAL PRODUCTS Ltd 4 March 1974 [29 Dec 1972] 60218/72 Heading B5N [Also in Division D1] Slivers of asbestos fibres are drafted and then bound with yarn or continuous filaments in the form of open helices of opposite hand to form a strand in which the majority of the fibres are parallel to the axis of the strand and the strand has little or no twist and a plurality of strands are assembled in side by side relation before or after impregnating them with a resin. The asbestos fibres are preferably long chrysotile fibres (i.e. Canadian classification group 1, 2 or 3) or crocidolite fibres. They may contain carbon fibres or 1 part in 9 of rayon fibres and are preferably corded formed into a sliver and bound with two opposed helices of 44 tex rayon multi-filament yarn. Other specified binding filaments or yarns are nylon, cotton, polyester, polypropylene, E glass asbestos yarn or metal wire. The binding filaments may comprise as little as 1 part in 30, e.g. 1 part in 18 of the strand. The resin may be a thermoplastic or thermosetting polymer suspension or dispersion. Specified resins are polystyrene, polymethylmethacrylate, polyvinyl chloride, copolymers of styrene with acrylonitrile, butadiene, acrylates or methacrylates; copolymers of vinyl chloride with vinyl acetate, vinyl fumarate or vinylidene chloride; phenolformaldehyde, ureaformaldehyde melamine formaldehyde or mixtures or copolymers thereof, silicone resins polyimides epoxides and polyesters. Preferably the thermosetting resins are rigid at room temperature after curing. In Examples 1, 3 a strand is impregnated by passage through a 45% aqueous solution of an alkali condensed phenolic resin, wound on to a 300 mm. square frame allowed to dry and partially cured by heating in an oven for 30 minutes at 90 C. Alternatively a plurality of strands may be impregnated and wound side by side on a drum. In Example 4 a cover fabric comprising weft of the helically bound strands and a warp of asbestos yarn is impregnated with a 50% alcoholic solution of a mixed ammonia/caustic soda catalysed cresolformaldehyde resin. In Example 5 a woven fabric comprising a warp of the helically bound strands and a weft of polypropylene multifilament yarn is impregnated with the resin of Examples 1-3. The asbestos warp of Example 4 and the polypropylene weft of Example 5 constitute less than 5% by weight of the respective fabrics. Laminating, moulding.-Four sheets produced as in Example 1 are stacked with their strand directions parallel in a 300 mm. open ended mould and cured for 30 minutes at 3À85 MN in<SP>-2</SP> pressure and 150 C. The proportions by volume of the asbestos, resin and rayon are 51 : 46 : 3. In Example 4 four woven layers were arranged with the strands at 90 degrees to those in adjacent layers. A sheet of the impregnated parallel strands may be cut from a drum and strengthened or its transverse direction by (1) stitching or resin bonding to a light-weight open mesh glass tissue or glass, asbestos or organic yarn cloth or paper, (2) backing with an adhesive surfaced paper or (3) interleaving a thin corded asbestos felt with a parallel array of unimpregnated strands as the strands are wound on to a drum. The composite material is then cut from a drum and impregnated with resin.